Microstructure and mechanical properties of direct laser deposited DD98 superalloy

A non weldable Ni-based DD98 superalloy was manufactured by direct laser deposition (DLD). The as-built samples show a heterogeneous microstructure along the build direction, which is associated with energy input. High energy input results in the formation of columnar grains with <001> very well aligned to the build direction. However, a cluster of voids preferentially distributes along columnar grain boundary, leading to poor ductility (e.g., ∼2.3% elongation) of the deposit as its strain direction is perpendicular to the build direction. Fine dendrite and γ′ precipitate are observed in the sample fabricated by low energy input, which is associated with fast cooling rate after solidification. Secondary phases excluding γ′, such as MC carbide and HfO₂ are observed in dendrite and interdendritic regions.